Terminal for heating units



NOV. 12, W R KgNG TERMINAL FOR HEATING UNITS Filed March 28, 1927ATTQRNEY L Patented Nov. 12, 1929 i UNITED sTATEs WILLIAM R. KING, FCMANSFIELD, OHIO,

ASSIGNOR, T0 fESTINGI-IO'USE ELECTRIC &

MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA TERMINAL FORHEATING UNITS Application led March 28, 1927. Serial No. 178,872.

My invention relates to electric heaters and particularly to encasedtubular heating units. An object of my invention is to provide anencased vtubular heating unit embodying a particularly simple andetlicient terminal construction.

Inpracticing my invention, I provide a tubular metal casing that may bebentlinto any desired shape, a helically-Wound resistor member thereinthat is held tightly therein by expansively-oxidizedlelectric-insulating material, and resilient pre-shaped terminal membersat each end of the tubular casing, an electric insulating bushing, and acable ter- 1'5 minal securedv to the projecting end of the resilientterminal wire.

In the drawings,

Fig. 1 is a view, partially in side elevation and partially inlongitudinal section, of an electric heater embodying my invention.

F ig. 2 is aview of an end portion, on an enlarged' scale, of anunfinished electric heater em odying my invention.

Fig. 3 is a View, in longitudinal sectiompf an end portion of Iacompleted heater embodying my invention. p y v Figs. 4 and 5 are views,in side elevation and in front elevation, respectively, of an endbushing, and p A 30` Fig. 6 is a view in section of the tubular heatertaken on line VI-VI of Fig. 1.

' An electric heater 11 comprises an outer tubular metal casing 12 whichmay be` of any kind of metal suitable for the temperature at' which itis to be operated. Thus, if the heater unit is to be operated atrelatively low temperatures a copper tube may bey used,

while a steel tube or a tube made of an alloy steel must be used if thetemperature is to be much higher.

A helically-wound resistor wire 13 is located withi'n thectubular casing12 and the respective turns thereof are slightly separated from eachother, as shown more particularly in Fig. 1 of the drawing.' Theresistor wire is held tightly Within the casing '12 by means of a mass14 of eXpansively-oxidized electric-insulating material consisting .ofmagnesium hydroxide or, oxide. The'V method of making or producingthecrystalline mass of electric-insulatng material is more particularlydisclosed and claimed in re-issued Patent No. 16,340 to C. B. Backer.Briefly, the method is'that of providing a helix of resistor wirelocated within an open helix 15 of a strip of initially-metallicmagnesium and the location of these parts within a tubular casing, suchas the casing 12, or a bundle of bars or wires of magnesium may belocated within the helix. The assembly is then subjected, for apredetermined length of time, to the action of high-temperature steamwhich effects a change of the metallic magnesium into magnesiumhydroxide or oxide, the material expanding to substantially 200% of itsinitial volume, whereby theresistor wire is tightly held within thetubular' casing. The mass 14 of electricinsulating material thusproduced 1s composed more particularly of a substantially solidcrystalline structure, whereby a highly efficient heat path from theresistor Wire to the casing is provided, in addition to holding Ythewire iirml-y within the casing. p

I prefer to make the longitudinal extent of the resistor helix 13 muchless than that of the casing 12, and I provide a resilient terminalconductor 16 for each end of the casing.

The outer-end portion of each of the terminal conductors 16 issubstantially straight, while the inner-'end portion is wavy or sinuousand is suitably connected to'an end of the resistor wire 13. The helix15 of initially-metallic magnesium extends to substantially the end \ofthe casing at each end thereof so as to surround both end portions ofthe respective resilient terminal conductors 1G. Upon treatment thereof,as hereinbefore described, the 'resilient terminal wire is tightly heldby the yeXpansively-oxidized magnesium hydroxide or oxide, substantiallyas shown in Fig. 1 of the drawing.

An'insulating bushing 17, of some suitable refractory material andhaving a (2o-'axial opening 18 therethrough, is provided at each end ofthe casing, the inner portion thereof being such as to closely fitwithin the casing 12, substantially as shown in Figs. 2 and 3 of thedrawings.

A cable terminal. l9fis provided at each end of the heaterand embodiesanouter portion to which a slpply-circuit conductor may be connected anan inner portion which may be folded over and around the end of the tersminal conductor 16 and soldered thereto. The inner` end of the cableterminal -19 abuts against the outer face of the bushing 17 in order tohold it securely in its operative poto crush the mass 14 of expansiveloxidized' magnesium h droxide or oxide uring the 20 final steps omanufacture of the heating units. The device embodying my inventionprovides a terminal wire that is heavier in lateral section than theresistor wire 13 and embodies two portions, one of these bein sinuous orbent, in order that the expande vmass of electric insulating materialmay hold the same and prevent longitudinal movement thereof relativelyto the casin 12. The outer-end portion thereofvis straight and exaotends through an opening in an end bushing, which bushing is effective.to prevent lateral movement ofthe terminal lead and also to retainth'ejmass 1414 within the casing. As the cable terminal 19 is securelymounted on the outer end of the terminal conductor 16, it

holds the bushing 17 in. its proper operative position and prevents anyleakage of the mass 14l of `'electric-insulating'material from/the'casing in case it becomes disintegrated to -magnesium t0 magnesiumIoxide in situ,

whereby the sinuous terminal conductor is secured 1n. place and providesan openingl through the oxide at the ends of the tube through which theoxidizing medium may pass until all of the metal about the resistorelement has been converted to magnesium oxide.

[2. A terminal for a tubular heating unit 'having a `tubular casin and aresistor therein, said terminal inclu ing an extended resillent terminalwlre havmgvan inner sinuous portion electrically connected to theresistor,

and a substantially straight outer portion, a mass ofelectric-insulating material expansively oxidized in situ in the casingand holding the resistor and the sinuous portion of the terminal wirethereinz a bushing of electric-insulating material 1n the' end of thetubular casing and having the straight` portion of the terminal wireextending therethrough, and a terminal secured to the terminal wire forholding the bushing in the cas- 1ng w In testimony whereof, I havehereunto subscribed my name this 22d da Iof March, 1927.

' WILLI R. KING.

6 a slight extent during the handling or the use thereof.

Since a portion of the lterminal conductor 16 is sinuous, a tortuouspassageway is rovided about and around the conductor w ich i" l 45extends through a portion of the magnesium oxide for a distancesubstantially coextensive Y with the length of the conductor (see Figs.1, 3 and 6). This passageway insures that steam will be permitted toflow through the 50 tube to convert the portion magnesium metal helix 15located in the middle portion of the i v tube 12 to the oxideofmagnesium in the event that the metal located in the ends of the tubehas been converted rst,which is usul 55 ally the'case.

Various modifications may be madel in the device embodying my inventionwithout departin from the spirit and. scope thereof and I esire,therefore, that only such limit, o0 tions shall be-A placed thereon asare imposed 1. The method of'making` a terminal strucl 4t -ture for aresistance element located in a. f

